cannot make 2 group by from a same group

trunk

inside a same group of group by, impossible to group by multi level

example, in opportunities, try to group by salesman and then team -> bug

Client Traceback (most recent call last):
  File "/home/aline/openerp/web/openerp-web/addons/web/common/dispatch.py", line 169, in dispatch
    response["result"] = method(controller, self, **self.params)
  File "/home/aline/openerp/web/openerp-web/addons/web/controllers/main.py", line 763, in read
    dict(context, group_by=group_by_fields), sort or False)
  File "/home/aline/openerp/web/openerp-web/addons/web/common/openerplib/main.py", line 339, in proxy
    *args)
  File "/home/aline/openerp/web/openerp-web/addons/web/common/openerplib/main.py", line 216, in proxy
    result = self.connector.send(self.service_name, method, *args)
  File "/home/aline/openerp/web/openerp-web/addons/web/common/openerplib/main.py", line 93, in send
    return getattr(service, method)(*args)
  File "/usr/lib/python2.6/xmlrpclib.py", line 1199, in __call__
    return self.__send(self.__name, args)
  File "/usr/lib/python2.6/xmlrpclib.py", line 1489, in __request
    verbose=self.__verbose
  File "/usr/lib/python2.6/xmlrpclib.py", line 1253, in request
    return self._parse_response(h.getfile(), sock)
  File "/usr/lib/python2.6/xmlrpclib.py", line 1392, in _parse_response
    return u.close()
  File "/usr/lib/python2.6/xmlrpclib.py", line 838, in close
    raise Fault(**self._stack[0])

Server Traceback (most recent call last):
  File "/home/aline/openerp/server/trunk/openerp/netsvc.py", line 440, in dispatch
    result = ExportService.getService(service_name).dispatch(method, auth, params)
  File "/home/aline/openerp/server/trunk/openerp/service/web_services.py", line 583, in dispatch
    res = fn(db, uid, *params)
  File "/home/aline/openerp/server/trunk/openerp/osv/osv.py", line 118, in wrapper
    return f(self, dbname, *args, **kwargs)
  File "/home/aline/openerp/server/trunk/openerp/osv/osv.py", line 172, in execute
    res = self.execute_cr(cr, uid, obj, method, *args, **kw)
  File "/home/aline/openerp/server/trunk/openerp/osv/osv.py", line 163, in execute_cr
    return getattr(object, method)(cr, uid, *args, **kw)
  File "/home/aline/openerp/server/trunk/openerp/osv/orm.py", line 2578, in read_group
    query = self._where_calc(cr, uid, domain, context=context)
  File "/home/aline/openerp/server/trunk/openerp/osv/orm.py", line 4418, in _where_calc
    where_clause, where_params = e.to_sql()
  File "/home/aline/openerp/server/trunk/openerp/osv/expression.py", line 569, in to_sql
    q1 = stack.pop()
IndexError: pop from empty list